> ## Documentation Index
> Fetch the complete documentation index at: https://docs.abscissa.eu/llms.txt
> Use this file to discover all available pages before exploring further.

# Declarations and definitions

> Learn how declare and define variables.

## Declarations

Declarations let you assign a value to a variable:

```ms3 theme={"dark"}
x = 2

var = 25

y = x^2^ - 6x + 2
```

The syntax is: `{var name} = {expression}`

This makes the variable have the same value as the evaluated expression on the right.

It allows for reassignment later on (mutable variable):

```ms3 theme={"dark"}
# first assignment
x = 2

# second assignment
x = 3

# perfectly valid!

y = x
# y now resolves to 3
```

## Definitions

Definitions act exactly the same as declarations, but once the variable is assigned the value, the variable becomes immutable and it cannot be changed.

The syntax is: `{var name} == {expression}`

```ms3 theme={"dark"}
n == 6.62

# n cannot be changed anymore

# error
n == 4

# error
n = 3

# but it still can be used and even moved
n * 7 

b = n
b = 3
# valid!
```

## Locking

Locking is the practice of making a mutable variable, immutable. It is done by:

```ms3 theme={"dark"}
# initial assignment
x = 3

# locking
x == x
```